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Bob Berman's strange universe: Enter the equinox

March 2007: The stars never lie, and neither does the equinoctial Sun.
The vernal equinox.

It's one of those rare events that reminds people Earth is a planet in space. The media gets on board, too: TV weathermen are sure to say "days and nights are equal today," even though it's never true. Astronomers know better, realizing that atmospheric refraction bends the solar disk upward by its own diameter, letting us see the Sun even after it has set. This alters the day-night mix, boosting the actual annual sunshine by 1½ percent. It's demonstrated most clearly on the equinox, which has between 4 and 15 minutes more day than night.

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